Recently, as a semiconductor device becomes highly integrated, in a process for fabricating a semiconductor device, metal lines of about 0.25 μm or smaller in width are required. As a result, it is general to use a DUV (Deep Ultra Violet) photoresist film in forming the metal lines.
As the photoresist film is sensitive to a reflectance of the metal lines, the reflectance should be decreased to form a non-defective photoresist pattern. For the reason, an oxide-based antireflective coating (“ARC”) layer coated on the metal lines is widely used.
However, when an in-situ etching process of the ARC layer is performed in a metal etching chamber, functions of the device may be deteriorated due to a microloading effect between a center area and an edge area of a wafer or substrate. The microloading effect becomes more serious in a far edge area being away from the center area.
As an approach for decreasing the microloading effect, there has been proposed a process for improving a uniformity of metal lines. However, such a process has a limitation in overcoming a difference in etching rate between areas of the wafer. The problem is closely related with a deposition of polymers in the chamber. Especially, when a Si—X based ARC material is deposited in the chamber, such phenomenon becomes more severe.
FIGS. 1A and 1B illustrate cross sectional views showing states after etching of an ARC layer 2 and after etching of metal layers 3 and 5, respectively.
As shown in FIG. 1A, in etching the ARC layer 2, the metal layer 3 in a center area of a wafer 4 is exposed earlier than in an edge area of the wafer since the etching rate is higher at the center area than at the edge area.
Also, referring to FIG. 1B, after etching of the metal layer 3, the TiN layer 5 in the edge area is exposed less than in the center area.
That is, in such a conventional process, the etching rate of the ARC layer is greater in the center area than in the edge area so that the metal layer may be excessively etched and there may occur an underetch in the edge area.
When comparing the etching rates in the far edge area and the center area on the basis of a 10 mm wafer edge exclusion, experimental results indicate that the etching rate difference between the edge area and the center area is 1400 Å/min or more.